linux-kernel - Re: Break doesn't work on a CP2105

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Message-ID: <ZGtZKCvo71woGf9T@hovoldconsulting.com>
Date:   Mon, 22 May 2023 13:59:36 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Corey Minyard <minyard@....org>
Cc:     Craig Shelley <craig@...rotron.org.uk>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-usb@...r.kernel.org
Subject: Re: Break doesn't work on a CP2105

Hi Corey,

and sorry about the late reply on this.

On Wed, Apr 26, 2023 at 03:04:03PM -0500, Corey Minyard wrote:
> I have a development board with a CP2105 on it, and I was trying to send
> a break to it to do a sysrq.  And it wasn't working.
> 
> I have verified that the target driver works by setting a really slow
> baud rate and sending something with a lot of zero bits.  It got breaks
> just fine.
> 
> If I use TCSBRK, it seems to just send a short time with zeros, not
> even a full character's worth.  It receives a valid character with the
> top few bits set.  If I use TCSBRKP with a longer time, like 2.5
> seconds, it waits the whole time, then at the very end it gets the
> character as with the shorter break.
> 
> I can't find a programming manual for the chip, and I'm not sure what's
> going on.

I just verified that break works on the first port of my cp2105 but not
on the second one (I seem to receive the last characters sent instead).

Apparently this is expected as the datasheet (AN571) says the following
about the SET_BREAK command:

	This command is not supported on the second CP2105 interface.

Which port are you seeing this behaviour with?

Johan